In the state of the art, automatic transmissions, particularly for motor vehicles, are comprised of planetary gear sets that are shifted by means of friction elements or, as the case may be, shifting elements such as clutches and brakes and are usually connected to a starting element that is subject to a slip effect and are optionally connected to a lockup clutch, such as a hydrodynamic torque converter or a fluid clutch.
Automatic transmissions of this kind are known, for example, from DE 199 49 507 A1 by the applicant: a multi-step transmission in which, on the driveshaft, two non-shiftable, front-mounted gear sets are provided, which on the output side produce two speeds, which in addition to the speed of the driveshaft, can optionally be shifted using a shiftable double planetary gear set that acts on the driveshaft by means of selective engagement of the shifting elements, so that in order to shift from one gear to the next higher or lower gear, only one of the two previously actuated shifting elements must in each case be engaged or disengaged. In this way, by using five shifting elements, seven forward gears can be achieved, and by using six shifting elements, nine or ten forward gears can be achieved.
Furthermore, from DE 102 13 820 A1, a multi-step automatic transmission with eight forward gears and one reverse gear is known, which comprises a first input path T1 of a first gear ratio; an input path T2 that has a greater gear ratio than the first input path T1; a planetary gear set of the Ravigneaux type with four elements, wherein the order of the four elements in a rotational speed diagram are: a first element, a second element, a third element, and a fourth element; a clutch C-2 that transmits rotation of the input path T2 to the first element S3; a clutch C-1 that transmits rotation of the input path T2 to the fourth element; a clutch C-4 that transmits rotation of the input path T1 to the first element; a clutch C-3 that transmits rotation of input path T1 to the second element C3; a brake B-1 that engages the fourth element; a brake B-2 that engages the second element; and an output element that is coupled to the third element S3.
Furthermore, a 9-gear multi-step transmission is known from DE 29 36 969 A1. It comprises eight shifting elements and four gear sets, wherein one gear set serves as a front-mounted transmission, and the main transmission has a Simpson set and an additional gear set that serves as a reversing gear.
Other multi-step transmissions are known from the applicant's DE 102005010210 A1 and DE102006006637 A1.
Automatically shiftable planetary vehicle transmissions in general have already been described many times in the state of the art and are subject to constant development and improvement. These transmissions should therefore require less complexity of construction, in particular a smaller number of shifting elements, and with sequential shifting, it should be possible to avoid double shifting, so that during shifting within defined gear groups, only one shifting element is engaged at any given time.
From the applicant's not yet published DE 102008000428.3, a multi-step planetary transmission is known, which has a drive and an output that are arranged in a housing. In the case of this known transmission, at least four planetary gear sets are provided, henceforth referred to as first, second, third, and fourth planetary gear set; at least eight rotatable shafts, henceforth referred to as driveshaft, output shaft, third, fourth, fifth, sixth, seventh, and eight shaft; as well as at least six shifting elements, comprising brakes and clutches, whose selective engagement produces different gear ratios between the drive and the output, so that preferably nine forward gears and one reverse gear can be achieved.
In this way, the first and the second planetary gear set, which are preferably designed as minus planetary gear sets, form a shiftable front-mounted gear set, and the third and the fourth planetary gear set form a main gear set.
In the known multi-step transmission, it is provided that the carriers of the first and second planetary gear set are coupled to each other via the fourth shaft, which is connected to an element of the main gear set; that the ring gear of the first planetary gear set is coupled to the sun gear of the second planetary gear set via the eighth shaft, which can be detachably connected via a first clutch with the driveshaft; and that the sun gear of the first planetary gear set can be coupled by means of the third shaft via a first brake to a housing and can be detachably connected via a second clutch with the driveshaft, in which case the ring gear of the planetary gear set can be coupled by means of the fifth shaft via a second brake to a housing of the transmission. In addition, the seventh shaft is permanently connected to at least one element of the main transmission and can be coupled via a third brake to a housing of the transmission, in which case the sixth shaft is permanently connected with at least one additional element of the main gear set and can be detachably connected via a third clutch with the driveshaft; the output shaft is permanently connected to at least one additional element of the third gear set.
In the known transmission, the fourth shaft is preferably permanently connected to the ring gear of the planetary gear set, in which case the sixth shaft is permanently connected to the ring gear of the fourth planetary gear set and the carrier of the third planetary gear set, and can be detachably connected via the third clutch to the driveshaft. In addition, the seventh shaft is permanently connected to the sun gears of the third and fourth planetary gear set and can be coupled via the third brake to a housing of the transmission. The output is supplied by means of the output shaft being permanently connected to the carrier of the fourth planetary gear set. In addition, the third and fourth planetary gear can be combined into, or, as the case may be, reduced to a Ravigneaux set with a common carrier and a common ring gear.